1. Field of the Invention
This invention relates to a polyphonic digital synthesizer of periodic signals for the production of musical sound. More particularly, it concerns entirely digital synthesizers in which each periodic signal results from a succession of digital samples produced in particular from a wave form sample memory read at variable frequency and then converted into analog form.
2. Description of the Prior Art
Such synthesizers have already been described in French patent applications Nos. 7607419 of Mar. 16, 1976, 7720245 of July 1, 1977, 7832727 of Nov. 21, 1978, and in first certificate of addition number 7907339 of Mar. 23, 1979.
Each sample is produced from a set of digital data such as instantaneous phase, current amplitude (signal envelope), harmonic or octave row, analog output path, etc., which are stored in a block of memories. Each sample therefore results from the reading of a block of memories. This same block is the source of a complete periodic signal, by virtue of the periodic reading of this block and simultaneous updating of the instantaneous phase datum which it contains.
All of the samples of all of the periodic signals are produced sequentially and cyclically in a series which results from connecting the reading of the memory blocks.
Given that a complex output sound can be considered as the sum of a certain number of elementary periodic signals, e.g. sinusoidal, and given the polyphonic nature of the synthesizer, there are numerous memory blocks organized into an assembly called the "virtual keyboard." The synthesizer thereby generates a great number of signals automatically using the data inscribed in the "virtual keyboard."
To make up a complete musical instrument, such as an electric organ, the synthesizer is connected to keyboards, pedals, buttons, stops, and control means which register the data necessary for the generation of signals in the "virtual keyboard," according to actions taken with the keys, buttons, pedals, and stops, and as a function of time. In a quality musical instrument in particular, the development over time of the amplitude of each sound component must be made with great precision and according to given principles. But this need involves considerable work by the control means of the instrument, as well as great complexity of such means and a high cost for the circuits which compose them.